clock: add unsetctf functionality

Author: RustyBower

sopel/modules/clock.py

@@ -359,6 +359,17 @@ def update_channel_format(bot, trigger):
             "commands)" % (timef, set_command, channel_command))
 
 
+@plugin.command('unsetchanneltimeformat', 'unsetctf')
+@plugin.example('.unsetctf')
+@plugin.require_chanmsg
+@plugin.require_privilege(plugin.OP, message='Changing the channel time format requires OP privileges.')
+def unset_channel_format(bot, trigger):
+    """Unset the preferred time format for the current channel."""
+    channel = trigger.sender
+    bot.db.delete_channel_value(channel, 'time_format')
+    bot.reply('Successfully unset channel time format')
+
+
 @plugin.command('getchanneltimeformat', 'getctf')
 @plugin.example('.getctf #sopel', user_help=True)
 @plugin.example('.getctf', user_help=True)